Send her to the UU Church? Just kidding, but part of growing up UU was the comparative religion study that lasted throughout the middle school years. The book the church used was
Neighboring Faiths : Exploring Religions with Junior High Youth . If you don't know UU, it's not really a religion per se - they have no bones to pick with other faiths. Most of them are just trying to figure it out for themselves, whatever "it" is... They really design the comparative religion study to be interesting, non-judgemental, and informative.
It's a neat program, and the experience of exploring other faiths is so rewarding. Since the book is designed for an adult facilitator of no particular special or magical qualifications, I would think you could use it in a HS situation.
A little nostalgia from my yUUth:
Love is the doctrine of this church
The quest of truth is its sacrament
And service is its prayer
To dwell together in peace
To seek knowledge in freedom
To serve humankind in friendship
Thus do we covenant.
Man, that's nice stuff... Maybe it's time for my once-every-5-years visit soon...